1. Field of the Invention
The present invention relates to an actuator that may form part of a lithographic apparatus.
2. Background Art
A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g., comprising part of, one, or several dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned.
Lithography is widely recognized as one of the key steps in the manufacture of ICs and other devices and/or structures. However, as the dimensions of features made using lithography become smaller, lithography is becoming a more critical factor for enabling miniature IC or other devices and/or structures to be manufactured.
A theoretical estimate of the limits of pattern printing can be given by the Rayleigh criterion for resolution as shown in the following equation:
  CD  =            k      1        *          λ      NA      where λ is the wavelength of the radiation used, NA is the numerical aperture of the projection system used to print the pattern, k1 is a process dependent adjustment factor, also called the Rayleigh constant, and CD is the feature size (or critical dimension) of the printed feature. It follows from equation (1) that reduction of the minimum printable size of features can be obtained in three ways: by shortening the exposure wavelength λ, by increasing the numerical aperture NA or by decreasing the value of k1.
In order to shorten the exposure wavelength and, thus, reduce the minimum printable size, it has been proposed to use an extreme ultraviolet (EUV) radiation source. EUV radiation is electromagnetic radiation having a wavelength within the range of 5-20 nm, for example within the range of 13-14 nm, for example within the range of 5-10 nm such as 6.7 nm or 6.8 nm. Possible sources include, for example, laser-produced plasma sources, discharge plasma sources, or sources based on synchrotron radiation provided by an electron storage ring.
EUV radiation may be produced using a plasma. A radiation system for producing EUV radiation may include a laser for exciting a fuel to provide the plasma, and a source collector module for containing the plasma. The plasma may be created, for example, by directing a laser beam at a fuel, such as particles of a suitable material (e.g., tin), or a stream of a suitable gas or vapor, such as Xe gas or Li vapor. The resulting plasma emits output radiation, e.g., EUV radiation, which is collected using a radiation collector. The radiation collector may be a mirrored normal incidence radiation collector, which receives the radiation and focuses the radiation into a beam. The source collector module may include an enclosing structure or chamber arranged to provide a vacuum environment to support the plasma. Such a radiation system is typically termed a laser produced plasma (LPP) source.
It is usually necessary to move a substrate within a lithographic apparatus. The substrate may for example be moved from a substrate storage location to a location where the substrate may be patterned by the lithographic apparatus. An actuator may be used to move the substrate. One or more motors may be provided within the actuator. The one or more motors may generate contamination.
It may be desirable to reduce the likelihood that the contamination travels from the motor to a substrate, or to some other location in the lithographic apparatus.
According to a first aspect of the invention there is provided an actuator comprising a first part and a second part, the first part being configured to move relative to the second part, wherein a labyrinth seal is provided between the first part and the second part, the labyrinth seal being configured to restrict the flow of gas from a first side of the labyrinth seal to a second side of the labyrinth seal, wherein one or more inlets and one or more outlets are provided within the labyrinth seal, the one or more inlets being configured to provide gas to a location within the labyrinth seal and the one or more outlets being configured to remove at least part of the gas from a location within the labyrinth seal.
According to a second aspect of the invention there is provided a method of sealing an actuator using a labyrinth seal, the method comprising introducing gas into the labyrinth seal via one or more inlets connected to a location within the labyrinth seal, and removing gas from the labyrinth seal via one or more outlets connected to a location within the labyrinth seal.
Further features and advantages of the invention, as well as the structure and operation of various embodiments of the invention, are described in detail below with reference to the accompanying drawings. It is noted that the invention is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein